1. Field of the Invention
This invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) for obtaining sectional images of a desired site of an examinee. The sectional images are obtained by means of nuclear magnetic resonance signals (hereinafter referred to as NMR signals) released from the desired site of the examinee and received by a detecting surface coil in an opening of a gantry having a static magnetic field forming magnet and an inclined magnetic field coil.
2. Description of the Related Art
In an MRI apparatus for obtaining sectional images of a particular site such as the chest or the waist of an examinee, a surface coil is often employed for receiving the NMR signals since the surface coil provides excellent image quality and is easy to handle.
A conventional MRI apparatus using this type of surface coil includes, as main components thereof, a top board carrying the detecting surface coil, and a gantry defining an opening and having a static magnetic field forming magnet, an inclined magnetic field coil, a high frequency pulse generator and a signal transmitting coil. The apparatus further includes a vertically movable support for raising and lowering the top board and inserting the top board into the opening of the gantry, an image processor, and a system controller & RF unit.
Sectional images of a site of an examinee are obtained as follows.
First, the examinee is placed on the top board such that the site of the examinee to be photographed lies directly over the surface coil mounted in the top board. The top board is inserted into the opening of the gantry to a position in which the site of the examinee to be photographed lies centrally of the gantry.
Next, the inclined field coil is driven to superpose a linear magnetic field on a static magnetic field formed by the static magnetic field forming magnet, in order to provide positional information for use in tomographic image analysis. Then, the high frequency pulse generator is driven to generate high frequency pulses for exciting nuclear magnetic resonance in the examinee's body. NMR signals subsequently generated are received by the detecting surface coil.
Finally, the image processor prepares sectional images of the photographed site of the examinee based on the NMR signals received by the surface coil. The operations of the various components of the above apparatus are controlled by the system controller & RF unit.
However, with the construction having the detecting surface coil mounted in the top board, when photographs are taken of the site displaced from a sensitivity zone of the surface coil, or when a different site is to be photographed, the site must be positionally adjusted relative to the surface coil again. This requires the top board to be withdrawn from the opening of the gantry once to lift the examinee or shift the examinee on the top board, which could be painful to the examinee.
To solve such a problem, a type of MRI apparatus has been developed which includes a surface coil contained in a slide case mounted in the top board. The operator of the MRI apparatus manually moves the surface coil for positional adjustment between the surface coil and the site to be photographed.
According to this apparatus, a positional adjustment between the surface coil and the site to be photographed may be effected while the examinee lies in the opening of the gantry, and by moving the surface coil within the top board. Since it is unnecessary to move the examinee on the top board, the positional adjustment between the site and the surface coil may be carried out without distressing the examinee.
However, such an apparatus has the following disadvantage.
During a photographing operation, the operator controls a console or the like in a scanner control room which is partitioned from a photographing room in which the gantry and other equipment are installed. With the apparatus having the surface coil contained in the slide case, as noted above, the operator manually moves the surface coil for positional adjustment between the surface coil and the site to be photographed. To do this, the operator must move from the scanner control room to the photographing room. This imposes an irksome operation on the operator.